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[aprssig] Fill-in Digis

Robert Bruninga bruninga at usna.edu
Fri Mar 24 16:49:04 UTC 2006


>I am still not convinced concept  of a 'fill-in' digi is 
>a valid one, as it can lead to stations that  are 
>visible, but not actually 'pingable' unless you 
>have intimate   knowledge of the network.  

The thing that most people overlook about fill-in
digis, is that the concept gives us a 2 tier tool
to balance the ability of a distant mobile "geting 
into a digi" compard to his ability to hear a digi.  
There is a huge inbalance here, And I mean BIG.

The Fill-in digi attempts to better balance that
situation.  THink of the tier of out-lying fill-in
digis as just like a big voice repeater with remote
site receivers. 

Please consider:
1) A mobile's ability to get into a big digi the
farther out from it he is, is *mostly* limiited
in his lack-of-ability to hit the digi strong
enough to overcome all the surrounding
QRM from all other digis and all other stations.

2) But he hears the digi just fine at the same
distant location.

The FILL-in digi being closer to him will pick up
his signal quite well and give it a better chance
of getting into the big digi.    But, being a fill-in
digi, it will NOT add to the QRM by making
unneeded copies of 100% of all the other 
traffic on the channel.

>In fact I think I'm just going to  recommend 
>that to WIDE2-2 should be the default.

What this does is tie your hands at requiring
every digi to always digipeate 100% of 
everything.  When in many cases you dont
need all that duplicates to get packet OUT
to the mobile.  The problem is aways getting
the data *in* from the distant mobile.

So do not think of a fill-in-digi as being only
one way.  A fill-in is only placed where mobiles
cannot get in (but can still hear the big digi).
Remember, the mobile has NO QRM and
so if the digi transmits he will get it. 

If the area is an area where the mobile cannot
hear the big digi at all ever, then put a full
function digi there, not a fill-in one.  Though
you might want to set the full function digi
at low power so that it does serve its intended
area, but does not add to the mess at all
4 surrounding cities...

de WB4APR, Bob







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